Loud-speaking telephone set with low acoustic coupling



Sept. 27, 1949. s, PETERSON 2,483,231

LOUD-SPEAKING TELEPHONE sET WITH LOW ACOUSTIC'COUPLING Filed Aug. 17,1946 -I N VEN TOR. I EDWARD S. PETERSON ATTORNEY Patented Sept. 27 1949LOUD-SPEAKING TELEPHONE SET WITH LOW ACOUSTIC COUPLING Edward S.Peterson, Elmwood Park, Ill., assignor to Automatic ElectricLaboratories, Inc., 'Chi- 'cago, 111., a corporation of DelawareApplication August 1'7, 1946, Serial No. 691,279

8 Claims.

1 I This invention relates to improvements in acoustic devices, and morespecifically to certain relative arrangements of the loudspeaker meansand transmitter means in a set for a two way telephone system.

' It is an object of this inventionto design a simple and economicaltelephone set which will provide satisfactory operation at desiredvolumes when used by a party located at a distance from the sets.

It is a further object of this invention to provide improvedtransmission by producing a set which will minimize the strength of theacoustic coupling between the loudspeaker means and the transmittermeans, which coupling is inherent in this type of equipment.

It is a feature of this invention to employ a loudspeaker means with itsaxis normal to the axis of a cylindrical parabolic reflector so that thesound waves from the loudspeaker means leave the reflector as a beam ofparallel rays directed in a forward direction.

It is also a feature of this invention to position the loudspeaker meansat the cylindrical parabolic reflector focal point so that an equalamount of waves are emitted on both sides of a vertical plane passingthrough the focal point.

A further feature of the invention is the positioning of thetransmittingmeans in a manner such that a minimum of sound waves reflected by thecylindrical parabolic reflector will reach the transmitting means.

It is also a feature of the invention to position the axis of theloudspeaker means normal to the axis of the cylindrical parabolicreflector and the axis of the transmitter parallel to the axis of thereflector.

It is another feature of the invention to position the approximatecenter of the loudspeaker means at the focal point of the cylindricalparabolic reflector and the approximate center of the transmitter meanson a vertical line passing through the focal point.

' Novel features believed to be characteristic of the invention are setforth with particularity in the appended claims. The invention, togetherwith further objects and features thereof, will best be understood byreference to the following specification taken in connection with theaccompanying drawings comprising Figures 1 and 2.

Figure 1 is a diagrammatic view of a speaker equipped with a cylindricalparabolic reflector for the radiation of sound waves emitted by thespeaker.

Figure 2 is a perspective view of a distant talkwaves of the reflector 2ing telephone set comprising an illustrative embodiment of thisinvention.

In Figure 1, a loudspeaker means 2 is positioned at the focal point of acylindrical parabolic reflector l. The reflector may be fashioned froma-rectangular sheet of metal or any other suitable reflector material sothat it forms a refle-ctor shaped as a portion of a parabolic cylinder.The loudspeaker means 2 is mounted with its approximate center locatedin a vertical line which passes through the foci of the cylindricalparabolic reflector and with its axis normal to the axis of thereflector. In this manner, an equal amount of waves are emitted on bothsides of the plane passing through the foci and the vertex of thereflector. The sound waves are reflected by the cylindrical parabolicreflector in a forward direction parallel to the axis as a beam ofparallel rays. Since a greater efficiency of sound waves is experiencedat the center of the loudspeaker means, viewing any horizontal plane, aconcentration of waves will result at the outer edges of the reflectorwhich become relatively weaker as the axis of the parabolic reflector isapproached. This manner of wave reflection produces a beam of waves witha so-called dead spot along the axis of the reflector.

Figure 2 in perspective illustrates the transmitting means 3 mounted oncabinet 4 with its approximate center on a vertical line passing throughthe foci of the cylindrical parabolic reflector l and having its axisparallel to that of the reflector. The loudspeaker means 2 is mounted ona baffle board it which is located along the axis of the reflector.

It may be readily observed that the position of the transmitting meansas narrated above places it in the plane where a minimum of radiatedwill be experienced. Therefore, the sound energy of the loudspeaker isunable to agitate the transmitting means sufficiently to initiatesinging in the circuit, this being the object of the invention.

The cabinet 4 houses a conventional amplifier having a reflector I, anon-off switch 6, a volume control I, a dialing means 8 with connectionsto a telephone line, and a talk-answer, dial key 9.

The reflector is fashioned in the form of a cylindrical parabola fromany suitable reflecting material. The vertical edges of the reflectorare attached to the vertical sides Of the cabinet and the horizontaledges are fashioned to effect a tight fit with the top and bottom innersurfaces of the cabinet on three sides by means of wood screws or thelike, the fourth side being in contact with the reflector.

The working mechanism of key 9 is positioned in a small cutaway sectionof loaflie mounting board 10. The on-oir switch 6 and volume control lhave arm extension controls passing beyond the reflector to theamplifier. The amplifier chassis is curved in conformance to the shapeof the parabolic reflector.

No particular specification is intended for the nature of thetransmitting means in as much as the arrangement is adapt-able tovelocity, crystal or dynamic microphones. The speaker means likewise maybe of varied types.

Although a particular embodiment of the in vention has been described,it will be understood that various modifications may be made therein,and it is intended to cover in the appended claims all suchmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A distant talking and listening telephone set comprising a focusingparabolic sound reflector, a telephone loudspeaker apparatus beingpositioned in said set within said reflector on avertical line whichpasses through the foci of said reflector and on a vertical planecoincident with the axis of said reflector so that a substantially equalvolume of waves from said loudspeaker is transmitted on either side ofthe plane, said speaker having its axis normal to the axis of saidreflector, and a transmitting means mounted on said set in such aposition that its axis is coincident with said reflector axis and sothat its approximate center lies on said vertical line, said set therebyeflective to operate with a minimum amount of feedback occurring in thetransmit-.- ting means.

2. In a loudspeaking telephone set, a parabolic reflector within the setshaped as a portion of a cylinder, a loudspeaker mounted within saidreflector at approximately the focus of the reflector and having itsaxis perpendicular to a plane passing through the focus and the vertexof the reflector, said speaker transmitting sound Waves approximately inequal volume on either side of said plane, and a microphone mountedabove said speaker having its axis also falling within said plane andits central point lying approximately above said focus, whereby theminimum amount of feedback occurs in the microphone resulting from wavestransmitted by said speaker.

3. In an acoustic device, a parabolic reflector therein, a loudspeakermounted in said reflector so that its center is located approximately ona vertical line which passes through the foci of. said reflector and ona vertical plane coincident with the axis of said reflector so that asubstantially equal volume of waves is transmitted on either side of theplane, said speaker having its axis normal to the axis of saidreflector, and a transmitting means mounted in the device in such aposition that its axis is coincident with said plane, said devicethereby effective to operate with a minimum of acoustic coupling betweensaid loudspeaker and said transmitting means,

a. In a loudspeaking telephone set, a parabolic reflector therein in theform of a cylinder portion, a loudspeaker positioned in said reflectoron '4 a line passing through the foci of said reflector and having itsaxis normal to the axis of said reflector, said reflector therebyeflective to create a vertical plane of minimum sound waves, saidvertical plane passing through the vertex and foci of said parabolicreflector, and a transmitting means whose axis is coincident with saiddead plane, said set thereby operative to reduce acoustic coupling ofsaid loudspeaker and said means.

5. In a loudspeakin telephone set, a parabolic reflector, a loudspeakermounted within said reflector whose approximate center lies on avertical line which passes through the foci of said reflector and beingpositioned on a vertical plane coincident with theaxis of saidreflector, so that a substantially equal volume of waves are transmittedto either side of said plane, and a transmitting means whose approximatecenter lies on said vertical line.

6. In a loudspeaking telephone set, a rectangular sheet of reflectingmaterial fashioned the form of a parabolic reflector having acylindrical shape, abaflie board mounted in a vertical plane coincidentwith the axis of said reflector, a speaker mounted on said baiile boardwith its approx},

mate center on a vertical line passing through the foci of saidparabolic reflector and with its axis normal to the axis of saidreflector, so that an equal amount of waves are transmitted to eitherside of said bafile board, said reflector thereby ef fective totransmita beam of .parallel rays with a so-called dead plane along theaxis of said parabolic reflector.

'7. In a system as claimed in claim 6, atransmitting means mounted withits approximate center located on said vertical line and in said deadplane, said set thereby effective to minimize acoustic coupling betweensaid transmitting means and said speaker.

8. In a loudspeaking telephone set, a cabinet, a sheet of reflectingmaterial fashioned in the form of a parabolic reflector, by having ashape similar to a parabolic cylinder portion, located in said cabinetand fastenedthereto at its outer edges, a bafiie board mounted in thecabinet along the axis of said reflector thereby dividing the enclosedre-.- flector area into two equal sections, a speaker mounted in theapproximate center of the baffle board, said speaker having itsapproximate center on a'vertical line passing through the foci of saidparabolic reflector and having its axis nor mal to the axis of saidreflector, and transmit-v ting means mounted on said cabinet in aposition such that a minimum amount of sound waves from said speaker.will reach said means.

EDWARD S. PETERSON.

REFERENCES CITED The following references are of record in the

